問71
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マルチタスクの説明として, 適切なものはどれか。
平成24年度 春期 ITパスポート試験 問71
テクノロジ系ソフトウェア › オペレーティングシステム
This question's explanation and your answers so far.
解説
問 71
Incorrectア
This describes a multi-core processor. It is a hardware approach that puts several processor cores, each composed of arithmetic circuits and the like, inside a single CPU (LSI) so that multiple operations can physically run at the same time; two cores is called dual-core, four cores quad-core. Multitasking is an OS function that holds even when there is only one CPU (a single core), so it is a different concept from the number of cores.
Incorrectイ
This describes grid computing — a distributed-processing approach that links multiple computers connected over a network so that as a whole they form a high-performance system. What carries out the work is not CPU time inside one machine but multiple computers scattered across the network, and that is the decisive difference from multitasking. Clustering is a related term, but both are about combining multiple computers, not about switching between processes inside a single machine.
Incorrectウ
This describes SIMD (Single Instruction Multiple Data), a scheme that performs the same processing on multiple pieces of data with a single instruction; it is a processor instruction scheme used where the same operation must be applied to large amounts of data, such as image processing and scientific or engineering computation. Its focus is “how instructions correspond to data”, whereas multitasking deals with “how CPU time is distributed among processes” — a completely different issue.
- エ
正解 Multitasking is a scheme in which the OS divides the CPU's processing time into small slices and allocates them to multiple processes (tasks) in turn, so that even though the work is really handled one at a time, it looks to the user as if several tasks are progressing simultaneously. Choice エ says exactly this — “allocates the CPU's processing time to multiple processes in turn, making the processes appear to run simultaneously” — so it is appropriate. The unit of time between switches is called a time slice (time-sharing), and at every switch the OS saves and restores the execution state, such as the register contents (a context switch). The key point is that multitasking is not a hardware matter of increasing the number of CPUs; it is an OS (software) function that shares one limited CPU over time. Being able to write a document while music plays and a file downloads in parallel is thanks to this mechanism.
ここがポイント
- Multitasking = an OS function that divides the CPU's processing time into small slices and allocates them to multiple processes in turn (time slice / time-sharing), making them appear to run simultaneously. It is a software mechanism that works even with a single CPU; saving and restoring the state at each switch is called a context switch.
- Learn to tell the confusing “multiple” terms apart: multi-core = several cores implemented in one CPU (hardware); grid computing = multiple computers on a network working together (distributed processing); SIMD = one instruction processing multiple data items (instruction scheme); multitasking = one machine time-sharing among multiple processes (an OS function).
用語